Screw extractor



D. C. FABEL Feb. 11, 1930.

' Filed Aug. 5, 8

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Patented Feb. 11', 1930 PATEN T OFFICE nomum 0. BABE, or cnnvnnmn, onro,assrenon. To run CLEVELAND 'rwrsr DRILL COMPANY, OF CLEVELAND, OHIO, ACORPORATION OF OHIO scaaw nxrnacroa Application filed August 3, 1938.Serial No. 297,271.

5 pipes, screws, etc., which have had their heads or outside portionstwisted or broken off without leaving a projection sufliciently long toenable their removal in the usual manner.

Devices of the character referred to usually consist of a taperedoperating portion which is provided with helically arranged ribs orlands and intermediate flutes or grooves, these latter having concavesurfaces so as not to interfere with the desired engagement between suchlands and the metal or other material of the part to be extracted. As atpresent manufactured, such tools are open to objections; in the firstplace, their strength is not always sufiicient to enable them' to re- :0sist the torsional stresses incident to normal' use, and in the secondplace, the landsor ribs sometimes dig too deeply into the broken elementwith the result that such element is expanded radially and itsextraction hindered, if not entirely prevented.

This invention, with the object of improving these tools and making themmore positive and certain in action as well as stronger, contemplatesroviding raised or convex portions interme 'ate the ribs or lands, suchportions serving to strengthen the body against torsional stresses andalso forming stops for preventing the lands from expanding the metal orother material of the part to be removed to such an extent as tointerfere with its extraction. In other words, the-extracting tool whichis the subject of this invention provides for the lands having aninitial and non-expanding bite followedby a substantially generaldistribution of pressure over practically the entire inner surface ofthe bore of the element being operated upon, this obviating the abovementioned obj ections and adapting such tools to more reliablyperforming their intended function.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the means hereinafter fully described and'particularly pointed out in the claims, the annexed drawing and thefollowing description setting forth in detail certainmechanism embodyingthe invention, such disclosed means constituting, however, but one ofvarious mechanical forms in which the principle of the invention may beused.

In said annexed drawing Fig. 1 is a partly sectional elevational viewshowing my improved extractor and illustrating its manner of use inremoving a broken set screw; and Fig. 2 is a transverse horizontalsection taken on a the line 2-2 of Fig. 1.

As best shown in Fig. 1, the extractor contemplated by my inventionconsists of a body having a polygonal shaped end 11 and a taperedoperating portion 12,/such portion being provided with a plurality ofhelical lands or ribs 13 and intermediate flutes or grooves 14. Suchgrooves are formed with raised or convex portions 15 which may connectwith the ribs 13 by themore or less concave surfaces 16 and whichdesirably have a central course with respect to the adjacent lands. Asshown in Fig. 2, such a tool in section presents the general appearanceof a substantially circular body. having radially extending points whichproject a short distance beyond the general circumference. If desired,however, the base circle of the lands ma be of smaller diameter than thecircle de ed by the raised portions or ridges '15,

plane indicated by this beingv the case when the surfaces 16'are Iwithin or below a circle outlined by the intermediate convexities. Whenbeing used, as for instance,'in extracting a broken-off set screw 17(Fig. 1),

such screw is first provided with a hole or socket 18 into which theextractor is inserted until the lands 13 engage withthe metal adjacentthe mouth of the bore; then as the extractor is turned by a Wrenchapplied to the end 11, the lands 13 bite into such metal, this beingstopped when a predetermined depth has been attainedand the raisedportions 15 come into contact with the Wall of such bore. When thishappens, not only is further biting by the ribs 13 prevented but a soliden-.

gagement is produced which enables sufficient force to be appliedwithout danger of expanding the Work or breaking the tool;

the tool, of course, being turned in the direction required forloosening the work and the lands leading in a counter directionrelatively to the threads.

It will be understood that a single tool will be satisfactory for use indrilled screws or pipes of a wide range of sizes and that theproportions and configuration of the lands and intermediate stops can bevaried as necessary for tools of difierent sizes or to regulate theextent of penetration which occurs before the ridges come into contactwith the wall of the bore. It will also be apparent that even in thesame tool the relations existing between circles defined by the outerfaces of the ridges, by the engaging parts of the lands,

and by the bases of the lands, may vary if different proportions aredesired for the different diameters provided for ufse in holes ofdifferent sizes.

For some purposes, it has been found that the most satisfactoryoperation is obtained whenthe helix angle is approximately thirty fivedegrees and the taper about one and one-half or two inches per foot. Butin general the helix angle can be between fifteen and sixty degrees andthe longitudinal taper between one and four inches per foot. Thesevalues for taper of the body andangularity of the lands have beenascertained experimentally and are such as to produce the most efficienttool in combination with the present improvements as above explained.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the mechanismherein disclosed, provided the means stated by any of the followingclaims or the equivalent of such stated means be employed.

I therefore particularly point out and dis tinctively claim as myinvention 1. An extracting tool comprising a body having a taperedoperating portion provided with helical lands and grooves intermediatesaid lands, said grooves having outwardly and transversely curvedsurfaces forming stops for limiting the penetration of said lands.

2. An extracting tool comprising a tapered operating portion providedwith a plurality of helically arranged ribs and grooves 'intermediatesaid ribs, said grooves having transversely convex partssforming stopsfor limiting the action of said ribs when penetrating the wall of thebore of the part to be extracted.

3. An extracting tool comprising a body provided with helically arrangedlands and ridges between said lands, said ridges serving to limit thepenetration of said lands and having spiral courses between such lands.

4. An extracting tool comprising a body having a substantially circularoperating portion provided with helical ribs, said ribs being disposedat an angle of approximately thirty-five degrees and having alongitudinal taper of between one and one-half and two inches per foot.

5. An extracting tool comprising a body having a substantially circularoperating portion provided with helical ribs, said ribs extending at anangle between fifteen and sixty degrees and having a longitudinal taperbetween one and four inches per foot.

6. An extracting tool comprising a body having helical ribs, said ribsextending at an angle of about thirty-five degrees and defining surfaceswhich taper about one and onehalf or two inches per foot, said surfacesbeing convex in radial directions.

An extracting tool comprising a tapered body having helical ribs andhelical convexities between said ribs, said convexities being adapted tocontact with the wall of a bore in order to limit the penetration ofsaid ribs into said wall.

8. An extracting tool comprising a body having helical ribs and helicalridges between said ribs, a circle drawn through the bases of said ribsbeing coincident with a circle drawn around said ridges.

9. An extracting tool having a tapered and cross-sectionally circularbody provided with helical lands.

Signed by me, this 27th day of July, 1928.

DONALD C. FABEL.

